underpowering amp/sub/speaker. problem?

Using a 60-watt rated speaker with a 50-watt amp wouldn't be considered "under-powering". In any case, there's no real problem with using any speaker with a lower-rated amplifier, as long as you're able to play it as loud as you want without serious distortion.

With your sub amp, you need to check the "2-ohm" power rating of the amp, not the "4-ohm" rating. Yes, you have 4-ohm speakers; but since you have two of them, the combined load at the amplifier will be 2 ohms. The output power at 2 ohms will be divided evenly between the two subs.

My problems are that I'm 18 and I don't have a job, I left school at 13-14 and never went back, I have no GCSE's and nothing else, I can't get a job to help my mum who is struggling every week to keep a roof over our head. I find it hard to meet new people, or to even leave the house as I feel that I have Agoraphobia and possible Asperger's Syndrome - just like my brother. Yeah life is hard, but I'm trying to pull myself together the best I can, one step at a time & all that.. just feel pretty worthless sometimes, suicidal thoughts have cropped up more than once.. but I don't think I have the balls to kill myself, or I would have done it already.

well your first question you answered your self has you can power your 6.5 speakers and it will not over heat

you will need a higher amp to power your subs to get them pounding